Fix script's idempotence & Ensure safe push

[7PH]

Why

I've noticed when running the tool multiple times, contributions are counted multiple times in the target account. This shouldn't be the case.

What

Proposal:

• Ensure the script's idempotence (versioning should be based on this once we reach 1.x.x)
• Use push rather than force push in the scripts/*-push.sh script to ensure we're not creating new commit hashes for old commits. Have an option to still use force-push, since that could happen if one of the tracked repository was itself force-pushed.